The development of rapid, portable, cheap, and/or easy-to-use detection devices for point-of-care application is oftentimes a challenge for the modern medical diagnostic industry to effectively diagnosis any number of diseases, including diseases that result in deaths of millions each year in developing countries. For example, conventional laboratory based technology, such as microarray, reverse transcription polymerase chain reaction (RT-PCR), etc. is relatively slow, employs multistep procedures, and/or uses bulky, expensive fluorescent detection units operated by trained technician. The cumbersome equipment requirements typically restrict the usage of such systems to the laboratory settings. The present disclosure provides for a nanomembrane based electrochemical nucleic acid detection platform that can be turned into a hand-held, portable device operated by workers with minimal instruction.
Rapid and portable devices for point-of-care application would allow for recognition of contamination and effective diagnosis of diseases that result in the deaths of millions each year in developing countries. The main challenges for the platform have been the elimination of sophisticated instruments and reagents, reduction in size to allow portability, acceptable detection sensitivity and robustness towards field sample variability, and sufficiently high assay rapidity to be compatible with portability. Presently, the genetic identification is mostly achieved by Enzyme-linked immunosorbent assay (ELISA), microarrays, and/or by real-time polymerase chain reaction (PCR). As previously noted, however, these conventional laboratory based technologies are relatively slow, employ multistep procedures, and use bulky and expensive fluorescent detection units operated by trained technicians. The cumbersome equipment requirements restrict the usage of such systems to the laboratory settings. Recent progress in dip-stick ELISA type assay is intended to circumvent the instrumentation and personnel demands, but its sensitivity remains unacceptable for field employment.
Electrochemical sensing with molecular probes functionalized onto the electrode sensor has also been developed as a candidate for label-free detection, particularly those that link the probe to the electrode with a linker that can enhance the electron transfer rate to the electrode once the target DNA has hybridized onto the probe. However, such self-assembled layer sensors remain unstable and hence not currently robust to the sample variability. Another label-free sensor technology that has been developed is the DNA chip technology which uses capacitance and field-effect transistor (FET) structures. Both techniques rely on the detection of the charges brought to the sensor surface by the hybridized target DNA. However, a recent survey has found that only DNA charges within the Debye electric double layer on the sensor can produce a capacitance or field-effect transistor signal. As the Debye layer is only a few nm thick under most practical conditions, there is a limit to the sensitivity of such capacitance and FET sensors, typically nano-molar. There is also a relatively significant fabrication cost typically associated with the capacitance and FET sensors. Electrochemical sensing and FET sensors all commonly suffer from long assay time as the hybridization reaction rate is limited by the diffusion of the molecules towards the probe, which can usually take hours for typical sample volumes.
As such, it is apparent that there is a need for an improved DNA/RNA detection technology. The present disclosure represents a new microfluidic technology that fully exploits the small spatial dimensions of a biochip and some new phenomena unique to the micro- and nanoscales. More specifically, the present disclosure addresses all the typical requisites for portable on-field applications: fast, small, sensitive, selective, robust, label- and reagent-free, economical to produce, and possibly PCR-free.